Role of processing aids in the extrusion of molten polymers

Product quality and, in general, processing windows and rates of production in the extrusion of molten polymers are limited by various flow instabilities (mainly melt fracture) that are observed at high production rates. While there still are unresolved issues in comprehending these phenomena, industry den-lands for process optimization dictate the employment of processing aids (PAS) for product quality improvement and energy requirement reduction. In this review paper, most commercially used processing aids (PAS) are discussed, namely, fluoroelastomers, stearates, small amounts of polymers blended with the process polymer, and the newly discovered boron nitride as pure and in combination with other fluoroelastomers. This paper focuses on the appropriate and optimum usage of the various PAS as well as on the mechanism that underlies their action for flow enhancement and instability elimination. Finally, numerous experimental observations are discussed, and several examples are illustrated.